I guess this has been beat to death, but I optioned to have the pirelli scorpion winters 275/40/20's installed all around. They look great, and dry road performance seems good. On the tire diameter issue, the stock fronts are 29.035" diameter (by spec), the stock rears 28.976, and the winters 28.661. It is hard to imagine the differential will have trouble managing the difference between the winters and the stock tires. Even a bit of uneven tread wear front to rear would create more of a strain.

I guess this has been beat to death, but I optioned to have the pirelli scorpion winters 275/40/20's installed all around. They look great, and dry road performance seems good. On the tire diameter issue, the stock fronts are 29.035" diameter (by spec), the stock rears 28.976, and the winters 28.661. It is hard to imagine the differential will have trouble managing the difference between the winters and the stock tires. Even a bit of uneven tread wear front to rear would create more of a strain.
I have done exactly the same thing and I gess we will see with time how it works out.